1. Field of the Invention
The present invention relates to a locking device, and, in particular, to a locking device which is adapted to be lockably secured to a towing pin or coupling element of a trailer so that unauthorized access to the coupling element and hence towing of the trailer is effectively prevented.
2. Description of the Related Art
Conventional trailer assemblies have a towing element or kingpin coupling element which protrudes in a downward direction from the bottom of the trailer bed. Tractors are designed to be coupled to and tow a trailer by rotatably encasing the kingpin. Coupling is achieved by inserting the kingpin of the trailer into a generally circular coupling device on the tractor. The circular coupling device is commonly referred to as a "fifth wheel". The trailer kingpin fits into a hole or slot in the center of the fifth wheel and is rotatably locked therein, thus enabling the trailer to be towed by the tractor.
There are many instances in which it is desirable to prevent a trailer from being towed by a tractor. For example, because trailer can be stolen or hijacked by simply attaching the trailer to a tractor and hauling away the trailer, trailer owners have a need for a device suited to prevent towing access to the trailer kingpin. Furthermore, law enforcement agents must periodically immobilize or "boot" trailers when there has been a legal infraction, such as a parking violation.
To prevent the unauthorized towing of a trailer it is known to attach a locking device to the kingpin of the trailer to prevent the fifth wheel from engaging it.
A typical prior art locking device includes a casing enclosing the kingpin of the trailer, a slidable locking bar within the casing for engaging the kingpin thereby securing the casing to the kingpin, and a lock mechanism for locking the locking bar in its engaged position. Known locking devices of this type are generally mechanically complicated and include a number of parts formed within the locking device. The complexity of such locking mechanisms makes them expensive, susceptible to a greater probability of mechanical failure, and difficult to use. Also one or more component parts may be misplaced rendering the unit unusable.
In another type of prior art device, shown in U.S. Pat. No. 3,600,914, a threaded studbolt rather than a locking bar engages the kingpin of the trailer. However, a separate tool for turning the studbolt is required to engage and disengage this device from the kingpin of a trailer, and the separate tool can be easily lost or misplaced. Also, in that device, access to the head of the studbolt is selectively blocked by a locking plug assembly which fits into a hole similar in size to that occupied by the studbolt. This further complicates the assembly and increases cost. Thus, that locking plug assembly suffers many of the same problems associated with the other, complicated locking mechanisms described above.